A variety of proposals and actual embodiments for optical communication, detection and ranging have been made. These include long range communications and relatively short distance transmission of information. It is important in most of these arrangements to have a high quality, i.e., nearly diffraction limited, high intensity, temporally coherent light beam. A laser can provide a high quality light beam, but may be limited in the power it can deliver to the beam.
For example, it is desirable to employ laser diodes for optical communication. These have low power consumption, can be rapidly switched, have very small physical dimensions, can be made economically, and produce a good quality light beam. The amount of power available from the laser diode, may be limited, however, by the possibility of damaging the laser at high power levels.
It is therefore desirable to combine the power of several lasers or optical gain elements, i.e., optical amplifiers, to enhance the power in a light beam. Individual laser diodes differ slightly from each other and may therefore lase at slightly different frequencies and are not temporally coherent. A technique is therefore desirable for providing optical coupling for several elements that provide optical gain for making the output beams of the optical gain elements temporally coherent.